Electric picture-transmitting apparatus



May 21, 1929.. w. 1.. OVERTON 1,713,6 8

ELECTRIC PICTURE TRANSMITTING APPARATUS Filed Dec. 29, 1924 .muuuuu flm a. J

INVENTOR WI. Oval/[0w ATTORNEY Patented May 21, 1929.

UNITED STATES WARNER L. OVERTON, OF BROOKLYN, NEW YORK, ASSIGNOR TO AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

ELECTRIC PICTURE-TRAN SMITTIN G APPARATUS.

Application filed December 29, 1924. Serial No. 758,715.

An object of my invention is to provide a new and improved system for generating an image transmitting current in an electrical image producing system. Another object of my invention is to provide etficient means for modulating acarrier current in accordance with the degree of shade of the successive elements of a picture or object an image of which is to be produced. Still another object of my invention is to provide a modulating system for efficiently modulating the current from a vacuum tube oscillator by means of a photoelectric cell. These and other objects of my invention will become apparent on consideration of an example of a system embodying the invention which I have chosen for presentation in the following specification taken with the accompanying drawing. It will be understood that the'invention is defined in the appended claims and that the following specification relates to the embodiment thereof shown'in the drawings. In this embodiment a carrier curr t is generated by a three electrode vacuum tube oscillator and a photoelectric cell is introduced in parallel with the plate of the plate circuit. The resistance of the cell is varied by the degree of shade of successive elements of the picture or object so as to modulate accordingly the output current from the oscillator.

In the drawings, Figure 1 is a diagrammatic sketch showing transmitting apparatus adapted to put a picture carrying current on a line, and Fig. 2 is a diagram of a modification.

Referring to Fig. 1, light from the source I is focused by the lens L on the opening in the screen A through which the light passes to the photoelectric cell P. This cell P is within a glass drum F round which the picture is wrapped in the form of a semi-transparentfilm. The drum F is fixed on an axial shaft D which is screw-threaded, so that by engagement with a suitable support the drum F is traversed slowly along its axis as it is rotated.

The vacuum tube oscillator O has the associated circuits, as plainly shown in the.

N, and a portion of their energy will be fed back into the grid circuit, so that the oscillatory currents will be self-sustaining. The energy for the oscillatory current output of the system is afforded by the plate circuit battery B in series with which is the iron core coil S. It will be seen that the circuit of the battery B branches at X and Y, one branch comprising the photoelectric cell P and'the other branch in parallel therewith completing the plate circuit of the oscillator Q. The high frequency oscillatory current in the plate circuit will be kept out of the coil S and out of the photoelectric cell P by the air core coil T and will go principally in the circuit through the plate and the coil V and the conductor Z. By the inductive relation between the coils V and IV this oscillatory current will be put through the amplifier Q, on the line J The amplitude of this oscillatory current would depend on the strength of the battery B, in the absence of the shunt from X through the photoelectric cell P. to Y..

As the'drum F rotates, successive elemental portions of the picture film pass in .helical order under the opening in the screen A, and accordingly the quantity of light falling on the photoelectric cell P is determined by the shade of these picture elements, and the resistance of the photoelectric cell will vary to correspond with the varying shade of the picture elements. This variation in the resistance through the cell P causes a variation in potential across the points X and Y and therefore varies the amplitude of the output oscillatory current. This system, as disclosed, puts on the line J a carrier current of a certain frequency with its amplitude varied to correspond with the varying shade of the successive elements of the picture.

The modification of Fig. 2 is adapted for modulation of a low frequency current. Here the carrierv frequencies are excluded from the coil S and battery B by virtue of the high inductance of the coil S, and from the cell P by reason of its high reactance, and the carrier current flows principally in the circuit through the plate, the condenser E, the coil V and the condenser shunted around it, and the conductor Z, and also in the shunted output circuit HG, which conducts the oscillatory current to the amplifier Q and thence to the line J.

. the light'on said cell in accordance with the shade of successive elements of a picture or.

object and thereby to modulate the oscillatory output current accordingly.

2. In combination, a three-electrode vacuum tube oscillator comprising a plate circuit and a battery therein, a branch circuit in parallel to at least a portion of said plate circuit, and light sensitive means non-inductively associated with said branch-circuit to vary its resistance in accordance with the shade of successive elements of a picture or object and thereby to modulate the plate circuit oscillatory current accordingly.

3. In combination, a three-electrode vacuum tube oscillator comprising a plate circuit and a battery therein, a photoelectric cell in parallel with the plate, a source of light casting a beam of light on said photoelectric cell, and means to vary the intensity of the light on said photoelectric cell in accordance with the degree of shade of successive elements in helical order to a picture wrapped in the form of a cylinder and thereby to modulatethe plate circuit oscillatory current accordingly.

4. In combination, a three-electrode vac uum tube oscillator comprising a plate circuit and a battery therein, a photoelectric cell in parallel with the plate, a path for oscillatory current connecting the plate and filament of said tube, means to confine the oscillatory currents to such path, means for extracting a part of the energy of such currents from said path, and means to vary the resistance of said photoelectric cell in accordshade of the sucessive elements of the picture or object.

6. An electro-optical system for setting up image currents comprising an oscillator enlployin a three electrode space discharge device, a igh inductance element in series with the space discharge gap of said device, and a I high impedance, light-sensitive element noninductively associated with said source and said high inductance element for varying the space current in said device in accordance with the shade of elemental areas of the field of viewwhose image is to be produced.

In testimony whereof, I have signed my name to this specification this 23rd day of December 1924.

WARNER L. OVERTON. 

